libbinder: Fix Trusty build from __ANDROID_VENDOR__

Fix a couple of minor issues from the addition of
__ANDROID_VENDOR__ to the Trusty build.

Bug: 242243245
Test: Build Rust binderRpcTest on Trusty
Change-Id: I834dd195149a42da39438af4d02a05190025497d
diff --git a/libs/binder/ndk/stability.cpp b/libs/binder/ndk/stability.cpp
index 73eb863..ca3d5e6 100644
--- a/libs/binder/ndk/stability.cpp
+++ b/libs/binder/ndk/stability.cpp
@@ -27,7 +27,7 @@
 #error libbinder_ndk should only be built in a system context
 #endif
 
-#ifdef __ANDROID_VENDOR__
+#if defined(__ANDROID_VENDOR__) && !defined(__TRUSTY__)
 #error libbinder_ndk should only be built in a system context
 #endif
 
diff --git a/libs/binder/trusty/rust/rules.mk b/libs/binder/trusty/rust/rules.mk
index 6de7eb5..d343f14 100644
--- a/libs/binder/trusty/rust/rules.mk
+++ b/libs/binder/trusty/rust/rules.mk
@@ -30,6 +30,9 @@
 	external/rust/crates/downcast-rs \
 	trusty/user/base/lib/trusty-sys \
 
+MODULE_RUSTFLAGS += \
+	--cfg 'android_vendor' \
+
 # Trusty does not have `ProcessState`, so there are a few
 # doc links in `IBinder` that are still broken.
 MODULE_RUSTFLAGS += \